I'd suggest that interval training with a turbo is more likely to achieve the desired improvements than a high speed ride to work. My commute is 13miles each way and I can go at a fair clip along most of it, but traffic lights, junctions and general traffic means it's more of a relaxed ride than if I could spend the 40minutes or so doing specific training.
That sounds sensible to me too. Most of my riding since my return has been on cyclepaths/mixed-use paths. They're great, and I hadn't realised there was so much accessible here - I have a 30-mile-ish city circuit lined up that will probably be only about 25% on road.
But it's not high-speed riding, and I really want to get my speed up. We have some very good roads here in Liverpool - even most of the major roads have decently wide lanes, mostly good surfaces, and good visibility, and I've been working out a few routes on those. But the problem is there are always traffic lights every few hundred metres, and I barely get my speed up before I'm having to slow down for the next set.
I have a turbo which I haven't used much yet, and it's going to be hard to stay indoors and use that now that the weather is improving, but I really think I need to get a few session on it.
Alan